In conventional storage systems, overall system and application performance is improved by caching data that is frequently accessed. In many applications, workloads benefit from and performance is improved if the cache uses a write-back mode. Cache data held in the write-back mode is sometimes protected against data loss by providing redundancy. The redundancy is commonly implemented with two Flash modules in a cache controller. Both Flash modules are permanently paired using mirroring, effectively reducing the available space to hold the cache data to a single Flash module. Given that only some host data benefits from the redundancy, inefficient use is made of the available space in the Flash modules.
It would be desirable to implement an elastic cache of redundant cache data.